Prime Minister Malcolm Turnbull believes voters will know of any changes to the tax system by the release of the May budget.

Mr Turnbull asserts that any outcome of a national conversation on budget repair -- which he says must included superannuation tax concessions -- would be made transparent prior to, or contained within, the May 2016 budget.

While he has not yet made his stance clear on whether Australia needs a rise in the rate of GST, Mr Turnbull believes any changes to the tax system would have to have a productivity benefit and compensate low-income earners.

The Coalition has faced significant backlash over a possible increase in the GST from 10 to 15 per cent, while also receiving criticism from Labor and the states for insufficient spending on schools and hospitals.

But Mr Turnbull hit back at the states, urging them to evaluate their own taxes, such as stamp duties.

"They (the states) have got to be prepared ... to go to their citizens and say ... we need to raise more money to spend on our schools and our hospitals and we are going to increase this state tax or that state tax'," he said on Friday.